Electrodes comprising an electrode substrate bearing a layer or coating of one or several metal oxides for use in electrolytic processes are well known. Common substrates include inter alia titanium, tantalum, nickel, and steel. Today, titanium is often used as electrodes but when titanium is negatively polarized, titanium hydride is formed which eventually seriously harms the stability of the electrode. Steel may corrode during or after stops in an electrolytic cell. Steel cathodes may also conduct atomic hydrogen whereby connection between steel cathodes and titanium based anodes in bipolar cells may need a back-plate to prevent formation of titanium hydride. U.S. Pat. No. 7,001,494 discloses further electrode material for use in a chloralkali cell.
The electrolytic production of alkali metal chlorate, and especially sodium chlorate, is well known. Alkali metal chlorate is an important chemical, particularly in the pulp and paper industry as a raw material for the production of chlorine dioxide that is widely used for bleaching. Conventionally, it is produced by electrolysis of alkali metal chlorides in non-divided electrolytic cells. The overall chemical reaction taking place in such cells isMCl+3H2O→MClO3+3H2 where M is an alkali metal. Examples of chlorate processes are described in inter alia U.S. Pat. No. 5,419,818 and EP 1 242 654.
One object of the present invention involves provision of an electrode which has improved performance in an electrolytic cell. One further object is to provide an electrode that is resistant to hydrogen evolving conditions and reducing conditions in alkaline environment and at least shorter exposures in oxidative environment. A further object of the present invention is to provide an electrolytic cell and a process for the production of alkali metal chlorate. It is particularly desired to provide such a cell in which the formation of oxygen and thereby danger of explosions is decreased while the operating conditions are facilitated. Yet another object of the present invention is to provide a cell in which a bipolar electrode or hybrids of bipolar and monopolar electrodes are mounted.
A further object of the present invention is to provide a cell in which the polarity of the electrodes can be reversed such that the electrodes successively can work as anode and cathode within a given period of time.
A further object of the invention is to provide an electrode improving the cathodic current efficiency when in operation in an electrolytic cell, particularly while reducing the cell voltage. A further object of the invention is to provide an electrode with reduced thickness resulting in material savings and optimization enabling an increased number of electrodes arranged in the same cell space whereby production may be increased without up-scaling an existing plant. A further object of the invention is to provide electrodes which may lower the metal loading of precious metals on an electrode substrate while substantially maintaining the performance of commercial electrodes. A further object of the invention is to provide an electrode that does not corrode whereby sludge which could be deposited on the anodes is not formed.